Comment by bruce511 | Hacker News Reader

Comment by bruce511 | Hacker News Reader

Unfortunately it's no as simple as just plugging a solar plant into the grid and standing back. The biggest difference between a solar plant, and a coal plant, is the ability to balance supply and demand through the day (or more specifically, through the night).

So, in effect, energy has to be stored during the day, and used during "unsunny" times.

Where I live we already have a pump-storage scheme in place. During the night, when demand for electricity is low, water is pumped uphill from one dam to another. During periods of high demand (typically early morning, and evening) water is released generating hydro-power to supplement the grid. It generates about 400MW of power - suitable for supplementing a city, but not for taking it "off the grid". It also doesn't scale particularly well - a 4GW plant would take a lot of water.

However, all is not lost. With "free" electricity it's fairly easy to split water into hydrogen and oxygen. Hydrogen isn't the easiest, or least damaging substance to work with, but it is certainly clean, storable, transportable and so on.

A power plant burning hydrogen as the fuel can run day and night. And a "hydrogen reservoir" would act as a natural capacitor - able to smooth the supply of energy to the plant.

Of course there are lots of uses for electricity which are not time-of-day sensitive. Desalination for example allows dry coastal regions (which usually get a lot of sun, and hence why they're dry in the first place) to become irrigated.

Solar power is a lot more useful than just domestic use, and I for one look forward to the day when it's cheap.

Another tactic that I quite like is using battery powered cars in combination with a smart grid to generate power during peak usage. If a car is plugged in and is fully charged, it will use a percentage of that to feed back into the grid.

Presumably, you'd give quite high incentives to doing this. If someone only charges their car when the grid has excess power, and allows up to 50% of that power to go back into the grid at peak usage, that electricity could even be free. There'd likely be a setting on your charging station to handle this.

You don't need many cars generating 5kW before you're talking about quite a serious amount of power.

Of course, there are problems with this approach - most people park their cars somewhere else during the day, the accounting is an issue, and it seems to be more suited to wind than solar, but I really like the idea of repurposing the massive batteries that we're going to have laying around anyway.

For reference, a Tesla battery pack holds 53kWh [1], which will supply an average home with power for two days [2]. So the numbers really do add up for using it to help during spikes.

[1]: http://en.wikipedia.org/wiki/Tesla_Roadster#Battery_system

[2]: http://www.eia.doe.gov/cneaf/electricity/esr/table5.html

The only problem with this of course is that the range of a car is already limited. Plugging in your car overnight, and then discovering half the charge is gone might be a tad, shall we say, unwelcome.

One could imagine though a big incentive (cost wise) not to charge the car during the day, or early evening but have the charger kick in after say 10pm. Then if your range is sufficient to get to work and back you're not motivated to charge during the day.

While all those batteries sitting there is somewhat appealing, the highest demand for grid power is also likely to be around the time you want to use your car.

> The only problem with this of course is that the range of a car is already limited. Plugging in your car overnight, and then discovering half the charge is gone might be a tad, shall we say, unwelcome.

Indeed.

However, electric cars could have a part to play in equalising electricity production & demand. Electric cars could be re-powered by removing the battery pack and inserting a new one (this would be done at the successor to petrol stations; obviously battery packs would all be the same size and have the same interface). The battery station would then need to recharge all its spare packs -- and it could do it at the times when electricity supply exceeds demand.

I would love that to happen but I doubt it. Batteries are too expensive and last a relatively small number of charges, so if you leave your battery in the station and they give you another, nobody says that this battery is not worn and it lasts very little

Actually, it's already being tried.

http://en.wikipedia.org/wiki/Better_Place

So, in effect, energy has to be stored during the day, and used during "unsunny" times.

Electricity demand is already way higher during the day than during the night. A good example besides the obvious of "lights" would be air conditioning.

Most likely, the amount of solar power built in such a case would converge to (typical peak power during the day) - (typical peak average power during the night), with existing technologies or other renewable technologies used to cover the remaining.

"Electricity demand is already way higher during the day than during the night."

yes and no. Obviously it'll differ from place to place, and climate to climate, but here the highest demand occurs in the early morning and the early evening. Both peaks are caused mostly by domestic consumption - hot water and food preparation being significant.

Now depending on the time of the year this may coincide with daylight, or night time. Either way solar performance at this time of day is poor.

Of course commercial use keeps demand up through the whole day, but during this time domestic use (including heating and cooling where required) is either minimal or sufficiently random to "smooth" the demand. There is also some use all through the night (lights being an obvious source, although more efficient lighting is becoming more common.) But there are also all-night commercial and industrial requirements.

What about of world-wide energy grid, so that the side of the earth with sunshine routes their left-over energy to the side without sun?

I realize this is currently a fantasy but would it ever be feasible or are there technical limitations preventing this from ever occurring?

Define "technical limitation"?

The most obvious issue that springs to mind is the difference in voltage supplied from country to country. In the US it's 110V, elsewhere it's usually 220V or 240V. So I suppose replacing every electrical appliance inside, or outside, the US isn't a "technical" limitation, but it's certainly a limitation of some kind.

That aside there are losses when electricity is "moved" - they further you move it the more you lose. (that's a simplification, but it'll do.)

Politically of course, there are limitations as well. Assuming the grid was mostly on land, each country becomes vulnerable to another country cutting it off. I'm not sure that the US for example would want to be dependent on Canada, or Russia, and I suspect the rest of South America may not like being vulnerable to Panama, and so on.

Most of the generation would probably occur in desert regions, and I'm thinking that's already a problem with an oil based economy.

That limitation is a little bit arbitrary - 110/240 are stepped down, post-transmssion voltages. In terms of interconnection/transmission between states there are ways around this. 50/60Hz poses a little bit more of a difficulty, perhaps... I'm no electrical engineer but there are apparently (inefficient?) ways to do this.

Japan seems to overcome the frequency issue somehow:

https://secure.wikimedia.org/wikipedia/en/wiki/File:Power_Gr...

Half of the country operates at 50Hz and the other half at 60Hz:

"In Japan, the western part of the country (Kyoto and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimizu Frequency Converter."

This has actually been a major issue in light of the recent damage from the earthquake/tsunami. Poser generation on the 50hz half of the country has been greatly diminished and the frequency matching stations have insufficient capacity to meet demand.

http://www.npr.org/2011/03/24/134828205/a-country-divided-ja...

http://en.wikipedia.org/wiki/Wardenclyffe_Tower

You've got the best chance if you do something like this. No wires = no evil countries cutting wires.

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